This invention relates generally to devices for bending surgical rods and more specifically to rod benders capable of bending a surgical rod into multiple different arc shapes.
Surgeons frequently use metal rods to facilitate the fusing of adjacent vertebrae in the spine to remedy a variety of spinal disorders. The spine, however, is curved, and the rods must often be bent to conform to the curvature of the bone in order to maximize affixation between the secured vertebrae. In some cases, pre-bent rods are employed by surgeons. However, commercially available pre-bent rods are provided only in specific sizes. While the general desired configuration of a rod for particular portions of the skeleton can be determined by x-ray and imaging techniques, in many instances it is desirable to confirm the desired configuration of the rod by visual inspection of the vertebrae at issue. Accordingly, it is desirable that the surgeon be able to shape bendable metallic rods during surgery to meet the specific anatomical fit requirements of a patient. Attempts have been made to bend rods into the desired configuration in the operating room during surgery. However, bending in many cases was effected employing pliers, vices, and hammers.
More sophisticated rod benders have been developed and are, in general, known, but many of such devices typically can bend the rod only to a single particular radius. One prior art device that can be used to bend the rod into one of three radii is disclosed in U.S. Pat. No. 5,490,409, entitled xe2x80x9cAdjustable Cam Action Rod Bender for Surgical Rodsxe2x80x9d. The handheld rod bender disclosed therein includes an adjustable cam with three positions for providing three different radii into which a rod can be bent. While this provides an advantage in that more than one arc radius is provided by the device, surgeons will frequently encounter the need to bend the rod into an arc having a radius that is different than that provided by this device.
Another prior art device, which can bend the rod into one of several desired curved shapes, is disclosed in U.S. Pat. No. 6,035,691, entitled xe2x80x9cAdjustable Rod Bending Device for a Corrective Spinal Rod which is Used in a Surgical Operation.xe2x80x9d The table-top rod bender disclosed therein has a plurality of adjustable rollers that when brought to bear against a straight rod, cause the rod to be bent into the curved shape defined by the relative positions of the roller ends. While providing a plurality of potential arc shapes, this device is time-consuming, inasmuch as each adjusting bolt must be positioned correctly before the rod is bent.
Therefore, there is a need for a rod bender that enables the rod to be bent into several differently dimensioned arcs.
There is also a need for a rod bender that enables analog adjustment of the dimensions of the arc into which the rod will be bent.
There is also a need for a rod bender that can be used to quickly set the dimensions of the arc into which the rod will be bent.
Other needs met by the invention not explicitly stated will be set forth and will be more clearly understood in conjunction with the descriptions of the preferred embodiments disclosed hereafter.
A rod bender of the invention includes a ram shaft that is movable along a shaft path that passes between two rollers. The distal end of the ram shaft has an arcuate rod contact surface, and the rollers each have a curved roller surface. Each of the rollers is positionable, in an analog manner, at a variety of positions along a respective roller path, relative to a distal position of the arcuate rod contact surface (the position of the arcuate rod contact surface when the ram shaft is in a distal rod engaging position). A straight rod positioned against the rollers so that it spans the space separating the rollers and crosses the shaft path, can be rammed with the ram shaft so that the rod is bent into an arc. More particularly, the rod is bent as the movement of the ram shaft pushes the arcuate rod contact surface forward against the center of the rod, while the curved roller surfaces prevent corresponding forward movement of the lateral portions of the rod.
The movement of the ram shaft along the shaft path is effected by operation of a lever mechanically connected to the ram shaft by a cam. Movement of the lever correspondingly moves the ram shaft between a proximal rod disengaging position (where the distal end of the ram shaft is backward of the rollers) and a distal rod engaging position (wherein the distal end of the ram shaft is forward of the rollers). When the ram shaft is moved from the rod disengaging position to the rod engaging position, the straight rod spanning the space between the rollers is bent as the distal end of the ram shaft moves forward of the rollers.
At least one dimension of the arc into which the rod is bent is determined by the position of the rollers relative to the distal position of the arcuate rod contact surface. The position of each roller along its respective roller path is adjustable in an analog manner to any of a plurality of positions on the roller path.
More particularly in a first preferred embodiment, each of the rollers is rotatably mounted to a distal end of a respective roller shaft, and each roller shaft has a proximal end that is rotatably mounted about a roller shaft hinge point forward of the ram shaft. For example, to bend the rod into a tighter arc shape, the rollers are brought farther forward along the roller paths (by swinging the roller shafts about the shaft hinge point, so that the angle between the curved roller surfaces and the arcuate rod contact surface is smaller) prior to setting the rod and moving the ram shaft forward. Or, for example, to bend the rod into a looser arc shape, the rollers are positioned farther backward along the roller paths (by swinging the roller shafts about the shaft hinge point, so that the angle between the curved roller surfaces and the arcuate rod contact surface is larger) prior to setting the rod and moving the ram shaft forward.
Further in the first preferred embodiment, the setting of each roller along its roller path is effected by rotation of a respective knob at the end of a respective roller adjustment shaft. Each roller adjustment shaft cooperates with a coupling pin to swing its associated roller shaft about the hinge point. More particularly, each roller adjustment shaft has a threaded portion, and each coupling pin has a bore that is correspondingly threaded, so that rotation of the roller adjustment shaft moves the coupling pin along the threaded portion. For example, clockwise rotation of the roller adjustment shaft moves the coupling pin forward along the threaded portion (i.e., away from the knob), and counterclockwise rotation of the roller adjustment shaft moves the coupling pin backward along the threaded portion (i.e., toward the knob). The cooperating threads prevent movement of the coupling pin unless the roller adjustment shaft is rotated (this secures the coupling pin at the desired location once the knob is released). Further, each roller shaft has a slot or bore within which the coupling pin fits to engage the roller shaft, so that when the coupling pin is moved along the threaded portion, the coupling pin pushes against the side of the bore to push the roller shaft to swing the roller shaft about the hinge point.
Alternatively, in a second preferred embodiment, each of the rollers is rotatably mounted to a support block that extends parallel to the plane and perpendicular to the shaft path. Movement of the support block, which movement is parallel to the shaft path, moves both of the rollers relative to the distal position of the arcuate rod contact surface. In this embodiment, the movement of each roller along its roller path (and the securing of each roller at a desired position along the roller path) is effected by rotation of a knob at the end of a roller adjustment shaft. The roller adjustment shaft has a threaded portion, and the support block has a bore that is correspondingly threaded, so that rotation of the roller adjustment shaft (about a longitudinal axis of the roller adjustment shaft) moves the support block along the threaded portion. The cooperating threads prevent movement of the support block unless the roller adjustment shaft is rotated (this secures the support block at the desired location once the knob is released).